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// XMLReader.java - read an XML document.
// http://www.saxproject.org
// Written by David Megginson
// NO WARRANTY!  This class is in the Public Domain.
// $Id: XMLReader.java,v 1.3 2004/11/03 22:55:32 jsuttor Exp $

package org.xml.sax;

import java.io.IOException;


/**
 * Interface for reading an XML document using callbacks.
 *
 * <blockquote>
 * <em>This module, both source code and documentation, is in the
 * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
 * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
 * for further information.
 * </blockquote>
 *
 * <p><strong>Note:</strong> despite its name, this interface does
 * <em>not</em> extend the standard Java {@link java.io.Reader Reader}
 * interface, because reading XML is a fundamentally different activity
 * than reading character data.</p>
 *
 * <p>XMLReader is the interface that an XML parser's SAX2 driver must
 * implement.  This interface allows an application to set and
 * query features and properties in the parser, to register
 * event handlers for document processing, and to initiate
 * a document parse.</p>
 *
 * <p>All SAX interfaces are assumed to be synchronous: the
 * {@link #parse parse} methods must not return until parsing
 * is complete, and readers must wait for an event-handler callback
 * to return before reporting the next event.</p>
 *
 * <p>This interface replaces the (now deprecated) SAX 1.0 {@link
 * org.xml.sax.Parser Parser} interface.  The XMLReader interface
 * contains two important enhancements over the old Parser
 * interface (as well as some minor ones):</p>
 *
 * <ol>
 * <li>it adds a standard way to query and set features and
 * properties; and</li>
 * <li>it adds Namespace support, which is required for many
 * higher-level XML standards.</li>
 * </ol>
 *
 * <p>There are adapters available to convert a SAX1 Parser to
 * a SAX2 XMLReader and vice-versa.</p>
 *
 * @author David Megginson
 * @see org.xml.sax.XMLFilter
 * @see org.xml.sax.helpers.ParserAdapter
 * @see org.xml.sax.helpers.XMLReaderAdapter
 * @since SAX 2.0
 */
public interface XMLReader {

  ////////////////////////////////////////////////////////////////////
  // Configuration.
  ////////////////////////////////////////////////////////////////////


  /**
   * Look up the value of a feature flag.
   *
   * <p>The feature name is any fully-qualified URI.  It is
   * possible for an XMLReader to recognize a feature name but
   * temporarily be unable to return its value.
   * Some feature values may be available only in specific
   * contexts, such as before, during, or after a parse.
   * Also, some feature values may not be programmatically accessible.
   * (In the case of an adapter for SAX1 {@link Parser}, there is no
   * implementation-independent way to expose whether the underlying
   * parser is performing validation, expanding external entities,
   * and so forth.) </p>
   *
   * <p>All XMLReaders are required to recognize the
   * http://xml.org/sax/features/namespaces and the
   * http://xml.org/sax/features/namespace-prefixes feature names.</p>
   *
   * <p>Typical usage is something like this:</p>
   *
   * <pre>
   * XMLReader r = new MySAXDriver();
   *
   *                         // try to activate validation
   * try {
   *   r.setFeature("http://xml.org/sax/features/validation", true);
   * } catch (SAXException e) {
   *   System.err.println("Cannot activate validation.");
   * }
   *
   *                         // register event handlers
   * r.setContentHandler(new MyContentHandler());
   * r.setErrorHandler(new MyErrorHandler());
   *
   *                         // parse the first document
   * try {
   *   r.parse("http://www.foo.com/mydoc.xml");
   * } catch (IOException e) {
   *   System.err.println("I/O exception reading XML document");
   * } catch (SAXException e) {
   *   System.err.println("XML exception reading document.");
   * }
   * </pre>
   *
   * <p>Implementors are free (and encouraged) to invent their own features,
   * using names built on their own URIs.</p>
   *
   * @param name The feature name, which is a fully-qualified URI.
   * @return The current value of the feature (true or false).
   * @throws org.xml.sax.SAXNotRecognizedException If the feature value can't be assigned or
   * retrieved.
   * @throws org.xml.sax.SAXNotSupportedException When the XMLReader recognizes the feature name but
   * cannot determine its value at this time.
   * @see #setFeature
   */
  public boolean getFeature(String name)
      throws SAXNotRecognizedException, SAXNotSupportedException;


  /**
   * Set the value of a feature flag.
   *
   * <p>The feature name is any fully-qualified URI.  It is
   * possible for an XMLReader to expose a feature value but
   * to be unable to change the current value.
   * Some feature values may be immutable or mutable only
   * in specific contexts, such as before, during, or after
   * a parse.</p>
   *
   * <p>All XMLReaders are required to support setting
   * http://xml.org/sax/features/namespaces to true and
   * http://xml.org/sax/features/namespace-prefixes to false.</p>
   *
   * @param name The feature name, which is a fully-qualified URI.
   * @param value The requested value of the feature (true or false).
   * @throws org.xml.sax.SAXNotRecognizedException If the feature value can't be assigned or
   * retrieved.
   * @throws org.xml.sax.SAXNotSupportedException When the XMLReader recognizes the feature name but
   * cannot set the requested value.
   * @see #getFeature
   */
  public void setFeature(String name, boolean value)
      throws SAXNotRecognizedException, SAXNotSupportedException;


  /**
   * Look up the value of a property.
   *
   * <p>The property name is any fully-qualified URI.  It is
   * possible for an XMLReader to recognize a property name but
   * temporarily be unable to return its value.
   * Some property values may be available only in specific
   * contexts, such as before, during, or after a parse.</p>
   *
   * <p>XMLReaders are not required to recognize any specific
   * property names, though an initial core set is documented for
   * SAX2.</p>
   *
   * <p>Implementors are free (and encouraged) to invent their own properties,
   * using names built on their own URIs.</p>
   *
   * @param name The property name, which is a fully-qualified URI.
   * @return The current value of the property.
   * @throws org.xml.sax.SAXNotRecognizedException If the property value can't be assigned or
   * retrieved.
   * @throws org.xml.sax.SAXNotSupportedException When the XMLReader recognizes the property name
   * but cannot determine its value at this time.
   * @see #setProperty
   */
  public Object getProperty(String name)
      throws SAXNotRecognizedException, SAXNotSupportedException;


  /**
   * Set the value of a property.
   *
   * <p>The property name is any fully-qualified URI.  It is
   * possible for an XMLReader to recognize a property name but
   * to be unable to change the current value.
   * Some property values may be immutable or mutable only
   * in specific contexts, such as before, during, or after
   * a parse.</p>
   *
   * <p>XMLReaders are not required to recognize setting
   * any specific property names, though a core set is defined by
   * SAX2.</p>
   *
   * <p>This method is also the standard mechanism for setting
   * extended handlers.</p>
   *
   * @param name The property name, which is a fully-qualified URI.
   * @param value The requested value for the property.
   * @throws org.xml.sax.SAXNotRecognizedException If the property value can't be assigned or
   * retrieved.
   * @throws org.xml.sax.SAXNotSupportedException When the XMLReader recognizes the property name
   * but cannot set the requested value.
   */
  public void setProperty(String name, Object value)
      throws SAXNotRecognizedException, SAXNotSupportedException;

  ////////////////////////////////////////////////////////////////////
  // Event handlers.
  ////////////////////////////////////////////////////////////////////


  /**
   * Allow an application to register an entity resolver.
   *
   * <p>If the application does not register an entity resolver,
   * the XMLReader will perform its own default resolution.</p>
   *
   * <p>Applications may register a new or different resolver in the
   * middle of a parse, and the SAX parser must begin using the new
   * resolver immediately.</p>
   *
   * @param resolver The entity resolver.
   * @see #getEntityResolver
   */
  public void setEntityResolver(EntityResolver resolver);


  /**
   * Return the current entity resolver.
   *
   * @return The current entity resolver, or null if none has been registered.
   * @see #setEntityResolver
   */
  public EntityResolver getEntityResolver();


  /**
   * Allow an application to register a DTD event handler.
   *
   * <p>If the application does not register a DTD handler, all DTD
   * events reported by the SAX parser will be silently ignored.</p>
   *
   * <p>Applications may register a new or different handler in the
   * middle of a parse, and the SAX parser must begin using the new
   * handler immediately.</p>
   *
   * @param handler The DTD handler.
   * @see #getDTDHandler
   */
  public void setDTDHandler(DTDHandler handler);


  /**
   * Return the current DTD handler.
   *
   * @return The current DTD handler, or null if none has been registered.
   * @see #setDTDHandler
   */
  public DTDHandler getDTDHandler();


  /**
   * Allow an application to register a content event handler.
   *
   * <p>If the application does not register a content handler, all
   * content events reported by the SAX parser will be silently
   * ignored.</p>
   *
   * <p>Applications may register a new or different handler in the
   * middle of a parse, and the SAX parser must begin using the new
   * handler immediately.</p>
   *
   * @param handler The content handler.
   * @see #getContentHandler
   */
  public void setContentHandler(ContentHandler handler);


  /**
   * Return the current content handler.
   *
   * @return The current content handler, or null if none has been registered.
   * @see #setContentHandler
   */
  public ContentHandler getContentHandler();


  /**
   * Allow an application to register an error event handler.
   *
   * <p>If the application does not register an error handler, all
   * error events reported by the SAX parser will be silently
   * ignored; however, normal processing may not continue.  It is
   * highly recommended that all SAX applications implement an
   * error handler to avoid unexpected bugs.</p>
   *
   * <p>Applications may register a new or different handler in the
   * middle of a parse, and the SAX parser must begin using the new
   * handler immediately.</p>
   *
   * @param handler The error handler.
   * @see #getErrorHandler
   */
  public void setErrorHandler(ErrorHandler handler);


  /**
   * Return the current error handler.
   *
   * @return The current error handler, or null if none has been registered.
   * @see #setErrorHandler
   */
  public ErrorHandler getErrorHandler();

  ////////////////////////////////////////////////////////////////////
  // Parsing.
  ////////////////////////////////////////////////////////////////////

  /**
   * Parse an XML document.
   *
   * <p>The application can use this method to instruct the XML
   * reader to begin parsing an XML document from any valid input
   * source (a character stream, a byte stream, or a URI).</p>
   *
   * <p>Applications may not invoke this method while a parse is in
   * progress (they should create a new XMLReader instead for each
   * nested XML document).  Once a parse is complete, an
   * application may reuse the same XMLReader object, possibly with a
   * different input source.
   * Configuration of the XMLReader object (such as handler bindings and
   * values established for feature flags and properties) is unchanged
   * by completion of a parse, unless the definition of that aspect of
   * the configuration explicitly specifies other behavior.
   * (For example, feature flags or properties exposing
   * characteristics of the document being parsed.)
   * </p>
   *
   * <p>During the parse, the XMLReader will provide information
   * about the XML document through the registered event
   * handlers.</p>
   *
   * <p>This method is synchronous: it will not return until parsing
   * has ended.  If a client application wants to terminate
   * parsing early, it should throw an exception.</p>
   *
   * @param input The input source for the top-level of the XML document.
   * @throws org.xml.sax.SAXException Any SAX exception, possibly wrapping another exception.
   * @throws java.io.IOException An IO exception from the parser, possibly from a byte stream or
   * character stream supplied by the application.
   * @see org.xml.sax.InputSource
   * @see #parse(java.lang.String)
   * @see #setEntityResolver
   * @see #setDTDHandler
   * @see #setContentHandler
   * @see #setErrorHandler
   */
  public void parse(InputSource input)
      throws IOException, SAXException;


  /**
   * Parse an XML document from a system identifier (URI).
   *
   * <p>This method is a shortcut for the common case of reading a
   * document from a system identifier.  It is the exact
   * equivalent of the following:</p>
   *
   * <pre>
   * parse(new InputSource(systemId));
   * </pre>
   *
   * <p>If the system identifier is a URL, it must be fully resolved
   * by the application before it is passed to the parser.</p>
   *
   * @param systemId The system identifier (URI).
   * @throws org.xml.sax.SAXException Any SAX exception, possibly wrapping another exception.
   * @throws java.io.IOException An IO exception from the parser, possibly from a byte stream or
   * character stream supplied by the application.
   * @see #parse(org.xml.sax.InputSource)
   */
  public void parse(String systemId)
      throws IOException, SAXException;

}
